C3

Water passes through a mesh screen to remove big bits like twigs. Chemicals added to make solids and microbes stick together and fall to bottom. Water filtered through gravel beds to remove solids. Water is chlorinated to kill of harmful microbes.

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What type of reaction happens when ethanoic acid is produced from ethanol?

Oxidation.

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To test for magnesium ions a student added sodium hydroxide to a solution of low sodium salt. What colour precipitate was produced?

White precipitate.

3 of 24

What are the stages of the Haber process?

Nitrogen and hydrogen are mixed together. Nitrogen and hydrogen react to produce ammonia. A mixture of gasses enters the condenser. Ammonia is separated as a liquid.

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Why are people against adding fluoride to tap water?

No freedom of choice, fluoride in toothpaste, too much can cause fluorosis.

5 of 24

Explain how scale forms on heating elements.

On heating, the calcium hydrogencarbonate decomposes forming a scale of insoluble calcium carbonate.

6 of 24

Suggest why scale on heating elements causes problems.

The scale reduces the efficiency of the heating element or the scale increases energy costs / uses more energy.

Sodium / hydrogen ions are present in the ion exchange resin therefore the water is softened because these ions take the place of calcium / magnesium ions that cause hardness in the water.

9 of 24

What is the general formula for alcohols?

CnH2n+1OH

10 of 24

When ethanol dissolves in water the solution formed is not alkaline. Why?

Ethanol has only covalent bonds in its molecule.

11 of 24

In terms of bond energies, explain why hydrogen can be used as a fuel.

Because when it reacts with oxygen more energy is released in bond making than used in bond breaking therefore the reaction releases energy or the reaction is exothermic.

12 of 24

In terms of electronic structures, explain why iodine is less reactive than bromine.

Iodine (atom) is bigger / outer electrons (level / shell) further from the nucleus so the forces attracting an incoming electron are weaker / there is more shielding of the forces attracting an incoming electron so outer electron gained less easily.

13 of 24

Explain how a reversible reaction reaches equilibrium.

Equilibrium is achieved when rate of the forward reaction is exactly the same as the rate of the backward reaction.

14 of 24

The modern periodic table is an arrangement of the elements in terms of their atomic structures. Explain how.

Because the elements are in order of number of electrons or proton number because the number of shells is the number of the period because the number of electrons in the outer shell is the number of the group, except in the case of the noble gases.

15 of 24

What is the difference between scale and scum?

Scale is formed when heat decomposes dissolved calcium / magnesium compounds to produce calcium carbonate or magnesium carbonate. Scum is formed when soap reacts with calcium / magnesium (ions) to form calcium stearate / magnesium stearate.

How did Mendeleev know there must be undiscovered elements and how did he take this into account when he designed the periodic table?

If placed consecutively, then elements would be in wrong group /have wrong properties so he left gaps.

22 of 24

Describe how Knowledge of the numbers of protons and electrons in atoms allow chemists to place elements in their correct order and correct group.

Elements placed in) atomic / proton number order. Elements in same group have same number of 0uter electrons. Number of protons = number of electrons. Reactions/(chemical) properties depend on the outer electrons.

23 of 24

In terms of bond energies, why is a reaction exothermic?

Energy released forming new bonds is greater than energy needed to break existing bonds.